In recent years, dry film resists have been widely used in many fields, for example, producing print boards.
It is well known to use a carboxyl group-containing high polymer binder as one of the materials for producing a dry film resist so as to enable-the treatment of said dry film resist with an alkali aqueous solution.
When a resist comprising a carboxyl group-containing high polymer binder is laminated on a copper-clad laminate, however, frequently it is observed with the lapse of time that the surface of the unexposed portion of the copper plate turns reddish brown (so-called red-change) after completion of development or under-development (or the formation of scum) occurs. The troubles tend to become serious during processing. It is sometimes observed in practice that a resist laminated on a copper-clad laminate is allowed to stand as such for several days. Thus, both the red-change and under-development, which might frequently cause under-etching or peeling of plating film, are serious problems.
There have been proposals to add certain additives to a photopolymerization system to prevent the aforesaid red-change or under-development. For example, JP-B-58-22486 and JP-A-61-194438 propose to use low molecular weight carboxylic acids such as citric acid or malonic acid therefor (The terms "JP-B" and "JP-A" as used herein respectively mean an "examined Japanese patent publication" and an "unexamined published Japanese patent application"). While it is true that the addition of the carboxylic acids is effective in relieving the red-change or under-development, when the carboxylic acids are added in small amounts, sufficient effects cannot be achieved. On-the other hand, when the acids are added in such a large amount as to attain satisfactory effects, the sensitivity is lowered or the alkali-resistance of the resulting resist is reduced. Thus none of the carboxylic acids is satisfactory as a red-change inhibitor.